An armory where gang members can exchange parts, weapons, bodies, etc. Players can put in a request for a particular item, or maybe it's an open exchange. I'm thinking at no cost to each other, as the member is already giving up coins by not selling the items.

Yet again I have gone and sold a part that I did not want or mean too.
Apart the obvious solution of “be more careful” what would really help would be the ability to tag a part/body as unsellable so as to avoid accidental sale.
Please for my sanity make it so.

Here we have:
(see title!!!) lol. Anyway I have a little guide for you here:
The Basics
There are five modes in game:
leagues, quick fights, bets, gang fights, and championship.
Your goal is to build the best machine using various parts (you cannot control your machine during fights!) and
1. Get through every championship stage
2. Get the most rating.
Quick Fights
The first mode in the game that you are introduced to, what happens in quick fights is that you are matched against an opponent (almost always a bot) and have to beat them.
You can win boxes through quick fights through getting three wins* (not nessessarily in a row) and these boxes are: (you can hold 4 boxes at a time)
1. The regular box. Contains 4 parts, coins , and a chance for toolboxes and gems. Takes 2 hours to open.
2. The super box. Contains 6 parts (some containing random bonuses) with more coins than a regular box, and of course a chance for toolboxes and gems.
Takes 6 hours to open.
*There is not a specific pattern to receiving these boxes. Crowns can also be received for every 5-win streak and will give a 1-2 star bonus to the part you normally would have gotten.
In terms of matchmaking, you can be matched up with someone in your stage, someone in your prestige, (similar stats) or someone with slightly lower stats than you. This is why people like to have a terrible body with a much better weapon when going into quick fights selected: to farm crowns...
and to get high win streaks. Your win streak is shown next to the quick fight button. You don't get much for getting high win streaks besides pride though:
you get more and more rating from winning quick fights until win streak 10.
Leagues
In leagues, you are matched up with 49 OTHER people in the same league, and the higher rating** you have, the higher up you will be, and the more rewards you get. Each league round lasts about 2 days.
There are five leagues: wooden, stone, bronze, silver, and golden. (Which I think makes no sense but whatever.)
For winning each league, you will get a legendary box.
The golden league rewards are:
(lowest tier) nothing
(above tier) regular box and 2 gems
(tier above that) super box and 6 gems
(tier above THAT) legendary box and I think 7 gems
(best tier) legendary box and I think 15 gems
**See rating
Bets
In bets, two machines are shown. You have to guess which one will win. You bet parts, and if you win, they get a random bonus (or more of the bonus it already has) and rating that depends on your prestige/stage. If you lose, you either lose the part, or can recover it for gems. The longer the time, the better the bonus. Longer bets also have more slots. You can get more slots and more bets, and better bonuses through skills. When the bet time runs out, you will watch the fight and see if the machine you bet on won. You can watch the bet at any time.
There are three types of bets: quick (4:30 mins.) long (4:30 hours) and super (5? Hours).
They more parts you bet, the more gems it takes to recover them. Recover cost also depends on how high the bonus is.
These bets are unlocked at:
Quick: from beginning, second one can be unlocked with skills at prestige 1.
Long: also from beginning, second one can be unlocked through skills at prestige 2.
Super: unlocked at prestige 5.
Gang Fights
Unlocked once you join a gang, you will be matched up with a random opponent and your goal is to beat as many opponents as possible. The fights are 3v3, and you can choose your machine before starting each fight. If you beat all three of your opponents' machines, you will move on the the next opponent, and receive trophies(which will be talked about later) and a small box containing two parts. There are ten opponents to beat before your opponents reset again over a 24-hour period.
Championship
The championship is a mode where you are put in a group with 14 other people and have to beat as many opponents as possible through each stage.
You have to assemble the best machine possible to beat as many of your opponents as possible and to acquire the most medals; (received for each opponent you beat) when the championship ends, the top 6 people will be promoted to the next stage. Medals can be taken from you anytime if one of your opponents beats you. Whatever your selected machine is is the machine you will fight with and your opponents will fight against.
There are 24 stages in total to go through, each contains better parts; and each time you promote through a stage, you will receive either a super or legendary box, and a sticker.
You can also instant promote through a stage by beating all 14 of your opponents. You can unlock new parts by going through the championship.
Once you reach stage 24, you have the option to prestige, and go back to stage one, losing all your parts, coins, toolboxes, and stickers. You keep all your rating, gems, and skills, and gain some rating, gems, prestige status, and unlock some new parts.
Those were just the modes and basics, I'll add more detailed stuff later!